A painting bought by a British naval doctor for 140 pounds ($218) in 1962 may now be worth as much as 10 million pounds if his descendant can prove it’s a Caravaggio.

The authenticity of “The Cardsharps” is at the heart of a lawsuit against Sotheby’s, which judged the artwork a 17th- century copy. Described as by “Caravaggio (After)” in the auction where U.K. Royal Navy Surgeon Captain William Glossop Thwaytes bought it five decades ago, the painting was sold again through the auctioneers in 2006 for 42,000 pounds.

The purchaser, the British collector Denis Mahon, has since declared the work an original and valued it at 10 million pounds, according to court documents in London. The surgeon’s descendant, Lancelot Thwaytes, is suing Sotheby’s over the valuation and the case is scheduled to go to trial next year.

“Caravaggio is a particularly difficult artist,” Charles Beddington, a London art dealer who was formerly head of Christie’s International Plc’s Old Master paintings department, said in an interview. “The quality of his execution is variable, and so he’s easy to copy.”

British courts have seen an increase in the number of art- related cases as collectors who buy pieces for investment are increasingly willing to sue to recoup losses, and because the authenticity of works of art is becoming easier to prove as more scientific tests are being used, said Samson Spanier, a London lawyer at 13 King’s Bench Walk who’s not involved in the case.

“English courts have been hearing art-related disputes since the 18th century, but several recent high-profile cases suggest a rise in art litigation,” Spanier said.

Dark, Dramatic

Authenticated works by Michelangelo Merisi da Caravaggio, who died at the age of 38 in 1610, rarely appear on the art market. No painting catalogued as being by the artist has appeared at auction this century. His dark, dramatic paintings are coveted by many wealthy art collectors for their rarity.

The price at which the painting sold in 2006 reflects that the art market believed it was a copy, Sotheby’s said in an e- mailed statement. Its classification of the painting as a replica is supported by a Caravaggio scholar and “several other leading experts in the field.”

“The catalogue in which the painting was included was distributed among the world’s leading curators, art historians, collectors and dealers,” the auction house said. “Had they deemed the attribution different to that given in the catalogue, the price realized would doubtless have reflected that.”

Baroque Period

If the “Cardsharps” is deemed authentic, it’d also be a rare copy for the Italian painter, regarded by many historians as the most innovative artist of the Baroque period. The piece in dispute, currently on view at the Museum of the Order of St. John in London, is nearly identical to one of the same name by Caravaggio that’s on display at the Kimbell Art Museum in Fort Worth, Texas. The paintings depict two boys playing cards, one of whom has extra cards tucked behind him in his belt.

William Glossop Thwaytes, who also owned another Caravaggio, considered his “Cardsharps” authentic, according to the lawsuit. The painting, an oil-on-canvas about 40.5 inches by 51.5 inches wide, hung at Thwaytes’s home in Penrith, Cumbria, in the north of England, until he died.

Mahon, who died in 2011 at the age of 100, was a well-known collector and art historian. He left 58 Italian Baroque-period paintings to public collections in the U.K. “The Cardsharps” wasn’t included in the bequest because of attribution issues.

Works of art whose true value is missed by cataloguers, known as sleepers, can create difficulties for auction houses once owners become aware of lucrative after-sales.

‘Bad Publicity’

A pair of English school canvases of dogs sold for 840 pounds in 1985 at the U.K. regional auctioneers Messenger May Baverstock. The paintings re-appeared five months later at Sotheby’s as the work of the 18th-century artist George Stubbs and sold for 88,000 pounds.

The U.K. Court of Appeal ruled in 1990 that the regional auction house, being the equivalent to a non-specialist medical general practitioner, wasn’t culpable. Cases involving sleepers at international auction houses such as Sotheby’s and Christie’s have mostly been settled before going to trial.

Lancelot Thwaytes claims Sotheby’s didn’t adequately test the painting or consult experts. At his request, the auction house conducted x-rays and other analyses of the piece, according to the lawsuit.

Boris Kustodiev

Sotheby’s “negligently failed to carry out appropriate research into the painting,” Thwaytes said in the lawsuit. “The defendant obtained no written report containing any expert analysis of the x-rays and failed to identify, and report upon, pentiments and painting techniques which were characteristic of an original work by Caravaggio.”

Lawyers for Thwaytes at Boodle Hatfield LLP declined to comment.

In another recent art case in the British capital, the Russian billionaire Viktor Vekselberg won a 1.7 million pound claim against Christie’s in July last year after he bought a painting he thought was by Boris Kustodiev, a Russian painter who died in 1927.

The judge ruled that the painting was “the work of someone other than” Kustodiev, and that Vekselberg’s Aurora Fine Arts Investment Ltd. had the right to return the painting to the auction house and recover the money he paid.

Another lawsuit was filed against Sotheby’s this month over a different issue facing auction houses. A direct descendant of an early 20th-century governor general of Hong Kong sued the London-based auction house when it emerged that a painting had been stolen from the family’s Irish estate, the Evening Standard reported. The New York branch of Sotheby’s withdrew the artwork, Winslow Homer’s “Children Under a Palm Tree,” from auction in 2009. The painting was valued at 100,000 pounds, the newspaper said.